Chair of Soil Physics, Bayreuth Center of Ecology and Environmental Research (BayCEER), University of Bayreuth, Bayreuth, 95447, Germany.
Biogeochemistry of Agroecosystems, University of Göttingen, Göttingen, 37077, Germany.
Plant Physiol. 2021 Oct 5;187(2):858-872. doi: 10.1093/plphys/kiab271.
Although the role of root hairs (RHs) in nutrient uptake is well documented, their role in water uptake and drought tolerance remains controversial. Maize (Zea mays) wild-type and its hair-defective mutant (Mut; roothairless 3) were grown in two contrasting soil textures (sand and loam). We used a root pressure chamber to measure the relation between transpiration rate (E) and leaf xylem water potential (ψleaf_x) during soil drying. Our hypotheses were: (1) RHs extend root-soil contact and reduce the ψleaf_x decline at high E in dry soils; (2) the impact of RHs is more pronounced in sand; and (3) Muts partly compensate for lacking RHs by producing longer and/or thicker roots. The ψleaf_x(E) relation was linear in wet conditions and became nonlinear as the soils dried. This nonlinearity occurred more abruptly and at less negative matric potentials in sand (ca. -10 kPa) than in loam (ca. -100 kPa). At more negative soil matric potentials, soil hydraulic conductance became smaller than root hydraulic conductance in both soils. Both genotypes exhibited 1.7 times longer roots in loam, but 1.6 times thicker roots in sand. No differences were observed in the ψleaf_x(E) relation and active root length between the two genotypes. In maize, RHs had a minor contribution to soil-plant hydraulics in both soils and their putative role in water uptake was smaller than that reported for barley (Hordeum vulgare). These results suggest that the role of RHs cannot be easily generalized across species and soil textures affect the response of root hydraulics to soil drying.
虽然根毛（RHs）在养分吸收中的作用已有充分的记录，但它们在水分吸收和耐旱性方面的作用仍存在争议。我们将玉米（Zea mays）野生型及其毛缺陷突变体（Mut；roothairless 3）在两种不同质地的土壤（沙土和壤土）中生长。我们使用根压室测量土壤干燥过程中蒸腾速率（E）与叶片木质部水势（ψleaf_x）之间的关系。我们的假设是：（1）RHs 扩展了根土接触面积，并减少了高 E 下干燥土壤中 ψleaf_x 的下降；（2）RHs 的影响在沙土中更为明显；（3）Mut 可以通过产生更长和/或更厚的根来部分补偿缺乏 RHs。在湿润条件下，ψleaf_x(E)关系呈线性，随着土壤变干，关系变得非线性。这种非线性在沙土（约-10 kPa）中比在壤土（约-100 kPa）中发生得更突然，基质势也更负。在更负的土壤基质势下，在两种土壤中，土壤水力传导率变得小于根水力传导率。两种基因型在壤土中的根长增加了 1.7 倍，而在沙土中的根厚增加了 1.6 倍。在两个基因型之间，没有观察到 ψleaf_x(E)关系和活跃根长的差异。在玉米中，RHs 在两种土壤中对土壤-植物水力的贡献都较小，它们在水分吸收中的作用小于报道的大麦（Hordeum vulgare）中的作用。这些结果表明，RHs 的作用不能轻易地在物种间推广，土壤质地影响根水力对土壤干燥的响应。
